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  1. #1
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    Question 2-stage furnace staging - furnace or thermostat control, or combination?

    I recently had a new Payne PG96VAT 2-stage/variable speed furnace installed along with a Honeywell small bypass humidifier and third generation Nest learning thermostat.

    The HVAC contractor ran new thermostat wiring to support the 2-stage connection of the Nest for the C,R,G,W1,W2, and Y connections.

    I was informed that for 2nd stage operation the thermostat is the master control, but if the temperature is not satisfied within a certain amount of time the furnace will take over and turn on the 2nd stage. Based on my understanding either the furnace or the thermostat should control the furnace staging and not both.

    In having read the installation manual it states that if a wire is connected to W2 on the furnace control board, then dip switch SW1-2 should be set to the ON position to allow the thermostat to control the furnace staging (low heat only operation). From the explanation I received, I suspect that SW1-2 is in the OFF position which is the adaptive heating mode, hence, why the furnace is able to kick on 2nd stage after a certain time and take over from the thermostat.

    I feel that this sort of defeats the purpose of having a 2-stage thermostat as the furnace will take over the staging after a few minutes which defeats the purpose of longer run time in 1st stage for comfort purposes.

    Should I have the HVAC contractor correct this or just leave it as is?

    Thanks in advance for any feedback.

  2. #2
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    Best to have the thermostat con troll staging only. No need for it to time up to second stage. Can actually lessen comfort. Have them reset it.
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  3. #3
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    what he said

  4. #4
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    Get rid of the Nest. I’ve had so much trouble with them that I refuse to let my customers use them with new equipment.
    Honeywell thermostats have beenreliable.
    AOP Rules: Rules For Equipment Owners.

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    Questions should end with a question mark "?" Statements end with a period "."

  5. #5
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    Thread Starter
    Thanks for the replies.

    Based on what I'm hearing I will need to have the technician come back and set the furnace up to allow the thermostat to control the staging.

  6. #6
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    Your comfort will increase a lot after you do.
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  7. #7
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    Quote Originally Posted by Big_Z View Post
    Should I have the HVAC contractor correct this or just leave it as is?

    Thanks in advance for any feedback.
    Yes, they may have overlooked that switch, have them come back. It’s their responsibility to make sure the settings are correct for the application.
    "The only true wisdom is in knowing you know nothing" Socrates

  8. #8
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    This is a 'Ford vs Chevy' discussion... and IMO the climate you are in has a bearing on it...

    Here in the South... furnaces are generally slightly oversized to get the air flow capacity for AC needs...
    We tend to let the furnace stage the heat... however we discuss this with the homeowner to determine what their comfort expectations are.

    If your thermostat wire was only 4 conductors before... pulling a new wire to get a 5th conductor for the C terminal... does resolve a lot of the NEST issues...
    OTOH... as many PRO's suggest...
    NEST are not good thermostats...
    Literally ALL the features can be had with other stats, which are more reliable!

    One more thing about NEST... it calls home and tells Google when you are home and when you are away...
    Do you really want that???
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *Cheap is not good, good is not cheap; however expensive is not a guarantee of quality!
    Choose your contractor wisely!

  9. #9
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    Thread Starter
    Thanks everyone for the feedback.

    I had my HVAC contractor come back yesterday as I told them I want the thermostat to explicitly control the furnace staging. They turned ON dip switch SW1-2 to allow the thermostat to control the furnace staging (low heat only operation).

    I noticed that since the change the furnace is running for longer (approximately 20 to 30 minutes for 1 degree Celsius climb) in first stage, and it only ever runs second stage when the temperature is about 1.5 to 2 degrees Celsius from set-point.

    On hindsight, I probably should have gone with a different thermostat like Honeywell, but the Nest was recommended to me by several friends.

  10. #10
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    The longer time the furnace runs is what provides the greater comfort. It minimizes the cool/cold draft feeling you an get right after a furnace shuts off.
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  11. #11
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    Quote Originally Posted by beenthere View Post
    The longer time the furnace runs is what provides the greater comfort. It minimizes the cool/cold draft feeling you an get right after a furnace shuts off.
    And IMO... the longer the furnace runs... the more it thoroughly stirs up the air (mixing it, for more even temps); as well as gently heating the surfaces of items in the home, so they do not consume heat between cycles.

    Longer run times are a good thing...
    However having the second state to provide a blast of hot air (when wanted) is a nice thing...
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *Cheap is not good, good is not cheap; however expensive is not a guarantee of quality!
    Choose your contractor wisely!

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